Six investigators will continue to study the cell and molecular biology of lymphoid cells. Cultured cell lines and somatic mutants derived from them will be used wherever possible. Immunologically important molecules from parental and mutant cells will be characterized structurally and functionally. Amongst the questions being addressed are: the origins and targets of NK cells, the biochemical basis of macrophage functions including anti-bacterial activity, the mechanism of unresponsiveness in leprosy, the nature and role of cross reactive idiotypes of anti-DNA antibodies in lupus, the molecular basis of MHC polymorphism and the structural basis of MHC function in cell-cell interactions and antigen presentation, and the molecular basis of the somatic generation of antibody diversity and gene rearrangement associated with B cell differentiation.